Apparatus and method for exfoliating graphite

ABSTRACT

An apparatus and method to exfoliate a graphite grain is described. A mixture of a graphite grain and an ice grain are transferred into a vessel. The vessel includes an agitator. The agitator agitates the mixture to induce a contact between the graphite grain and the ice grain. The contact between the graphite grain and the ice grain exfoliates the graphite grain.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation application of U.S. patentapplication Ser. No. 17/736,034, filed on May 3, 2022, which claims thebenefit under 35 U.S.C. § 119(e) of the filing date of U.S. provisionalapplication No. 63/184,176 filed on May 4, 2021, the contents of both ofwhich are incorporated herein by reference in its entirety.

FIELD

The present disclosure generally relates to an apparatus and method forexfoliating graphite, and, in particular, it relates to an apparatus andmethod for exfoliating graphite grains to produce graphene using a fluidmedium.

BACKGROUND

Since its isolation in 2004, graphene has been a highly sought-aftercommodity. Consisting of a single layer of carbon atoms, this materialhas been theorized and demonstrated to possess remarkable properties,including a high tensile strength, high flexibility, high thermalconductivity, and extremely high electrical conductivity. Theapplications for this material abound and increase with each year ofresearch and development.

However, the demand for graphene far exceeds the capability of existingtechniques for producing it. The first technique to produce graphene,known informally as the “Scotch tape method,” includes the steps ofemplacing a strip of tape on the surface of a graphite block and peelingit away to mechanically exfoliate a thin sheet of graphite, emplacing asecond strip of tape on top of the first strip of tape and peeling itaway to exfoliate a thinner sheet of graphite; this process is repeateduntil exfoliated flakes of monolayer graphene are finally affixed to astrip of tape. Although monolayer graphene may be produced, thistechnique requires an enormous expenditure of labor and time as well asthe consumption of copious amounts of tape and solvents to remove saidtape and isolate the graphene flakes. This process is also not onlytedious, time-consuming, and costly but not environmentally friendly dueto the waste produced.

Additional techniques have been developed in the years since theintroduction of the “Scotch tape method,” falling into the broadcategories of “bottom-up” and “top-down” methodologies. Bottom-uptechniques, such as Chemical Vapor Deposition, assemble graphenedirectly at a nanoscale from free carbon atoms. Bottom-up techniques arecapable of producing sheets of graphene of configurable size but arelimited by the fact that they produce only a single sheet of graphene ata time. Top-down techniques, such as the “Scotch tape method,” rely onthe fact that naturally occurring graphite already includes stackedlayers of graphene that are held together by weak van der Waals forcesand seek to exfoliate these layers to isolate the graphene. Van derWaals forces include attraction and repulsion between atoms, molecules,and surfaces, as well as other intermolecular forces.

Traditional exfoliation techniques, however, are also limited by theirefficiency as well as the quality of their final product. As previouslydiscussed, the “Scotch tape method” requires an inordinate expenditureof labor and material and is disadvantageous for large-scale, industrialproduction of graphene. Other techniques, such as chemical exfoliationand liquid phase shear mixing, may be feasible for industrial productionbut produce a final product that is either compromised by oxidation orlimited to a slow production rate that drives up the production cost.

High-energy techniques that may produce graphene at a high rate andquality include laser-induced graphene (“LIG”) and flash Joule heating(“FJH”). These techniques allow the use of non-graphitic base materialsthat contain carbon, such as rubber or organic waste, and may producegraphene at higher rates than previously discussed techniques. However,these techniques are limited by the intrinsic safety risk and cost ofhigh-energy systems.

Thus, there exists a high demand for novel techniques of producinggraphene that are safe and scalable to industrial levels. Further, asthe current price of graphene is a limiting factor for the introductionof novel products leveraging the many useful features of the material,there exists a demand for novel techniques of producing graphene thatare inexpensive.

SUMMARY

The following presents a simplified summary of various aspects of thisdisclosure in order to provide a basic understanding of such aspects.This summary is not an extensive overview of the disclosure. It isintended to neither identify key or critical elements of the disclosure,nor delineate any scope of the particular implementations of thedisclosure or any scope of the claims. Its sole purpose is to presentsome concepts of the disclosure in a simplified form as a prelude to themore detailed description that is presented later.

In an aspect of the present disclosure, an apparatus and method forexfoliating graphite to produce graphene is provided. A mixture istransferred into a vessel. The mixture includes a graphite grain and afluid medium. The vessel includes an agitator. The mixture may beagitated by an agitator to produce a contact between the graphite grainand the ice grain to exfoliate the graphite grain.

In an implementation, a mixture may be transferred into a vessel. Themixture includes a graphite grain and a fluid medium. The vesselincludes an agitator and a chiller. The mixture is chilled by thechiller such that the fluid medium at least partially solidifies into anice grain. The mixture is agitated by an agitator to induce a contactbetween the graphite grain and the ice grain to exfoliate the graphitegrain.

In an implementation, an apparatus to exfoliate a graphite grainincludes a vessel to contain a mixture. The vessel includes a chillerand an agitator. The mixture includes a graphite grain and a fluidmedium. The chiller is configured to chill the mixture to at leastpartially solidify the fluid medium into an ice grain. The agitator isconfigured to agitate the mixture to induce a contact between thegraphite grain and the ice grain to exfoliate the graphite grain.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure is illustrated by way of example, and not by wayof limitation, in the figures of the accompanying drawings, in which:

FIG. 1 illustratively depicts a series of contacts between a graphitegrain and a fluid medium at a molecular scale, in accordance with animplementation of the disclosure;

FIG. 2 illustratively depicts an apparatus for exfoliating graphite, inaccordance with an implementation of the disclosure;

FIG. 3 illustratively depicts an apparatus for exfoliating graphite, inaccordance with an implementation of the disclosure;

FIG. 4 illustratively depicts an apparatus for exfoliating graphite, inaccordance with an implementation of the disclosure; and

FIG. 5 is a flow diagram illustrating a method for exfoliating graphite,in accordance with an implementation of the disclosure.

DETAILED DESCRIPTION

Before the present subject matter is described in detail, it is to beunderstood that this disclosure is not limited to the particularimplementations described, as such may vary. It should also beunderstood that the terminology used herein is to describing particularimplementations only, and is not intended to be limiting, since thescope of the present disclosure will be limited only by the appendedclaims. While this disclosure is susceptible to differentimplementations in different forms, there is shown in the drawings andwill here be described in detail a preferred implementation of thedisclosure with the understanding that the present disclosure is to beconsidered as an exemplification of the principles of the disclosure andis not intended to limit the broad aspect of the disclosure to theimplementation illustrated. All features, elements, components,functions, and steps described with respect to any implementationprovided herein are intended to be freely combinable and substitutablewith those from any other implementation unless otherwise stated.Therefore, it should be understood that what is illustrated is set forthonly for the purposes of example and should not be taken as a limitationon the scope of the present disclosure.

As used herein, “fluid” refers to a continuous, amorphous substancewhose molecules move freely past each other and has a tendency to assumea shape of a container. Fluids include both liquids and gases. Fluidsmay flow under certain conditions, such as when exposed to pressure orgravity.

As used herein, “grain” refers to a particle of a solid material whoseconstituents (such as atoms, molecules, or ions) are arranged in ahighly ordered microscopic structure, forming a crystal lattice thatextends in all directions. A grain may include crystallographic defects,such as vacancies, dislocations, impurities, and interstitial additions.

As used herein, “exfoliate” refers to the action of dividing a grain ofa layered material. The layered material may include any number oflayers prior to exfoliation. During exfoliation, the grain is dividedinto a first new grain and a second new grain, with the number of layersprior to exfoliation divided between the first new grain and the secondnew grain. The action of exfoliation may continue upon the first newgrain and/or the second new grain to produce additional new grains.

As used herein, “graphene” refers to a single layer (“monolayer”) ofcarbon atoms, arranged in a hexagonal bond pattern. As used herein,“multi-layer graphene” refers to a structure consisting of between 2 and10 layers of graphene stacked upon each other and held together by vander Waals forces. As used herein, “nanographite” refers to a structureconsisting of between 10 and 1000 layers of graphene stacked upon eachother and held together by van der Waals forces. As used herein,“graphite” refers to a structure consisting of more than 1000 layers ofgraphene stacked upon each other and held together by van der Waalsforces. However, any of these terms may be used interchangeably and onemethod that produces particular layer(s) of graphene may also produceother layer(s) of graphene without departing from the spirit and scopeof the present disclosure.

As discussed above, graphene is a highly sought-after material withattractive properties. For instance, graphene flakes may be used as anadditive to other materials to raise their flexural or compressivestrength. In addition, its conductivity is being investigated for use insupercapacitors and as a replacement for copper in some applications.Preliminary research suggests that graphene may also be utilized as afilter in desalination systems at attractively low energy usage rates.

However, existing methods to produce graphene have been limited byfactors such as a low rate of production and high and costlyrequirements of labor and/or materials. Existing methods thatsuccessfully overcome the challenges of production and scalabilitysuffer from other challenges. As the most attractive characteristics ofgraphene are a result of its repeating hexagonal pattern of carbonatoms, the presence of defects can interfere with its utility. Forinstance, the benefits of graphene are reduced when the structure of thecarbon atoms is compromised by oxidation. While graphene oxide may bereduced to form reduced graphene oxide, the final product containsdefects which also reduce its efficacy. Furthermore, some methodsadvertised by suppliers as producing mono-layer graphene actuallyproduce multi-layer graphene or even nanographite, which hold in commononly a fraction of the beneficial effects of graphene. For example, thestrength and conductivity of graphene are reduced by the presence ofadditional layers.

The present disclosure addresses the challenges faced by existingsolutions by introducing a method and apparatus for exfoliating graphiteto produce graphene which is highly scalable, requires a low cost oflabor and materials, may produce a high-quality finished product, andpresents minimal safety risks.

As described herein, the adhesive properties of a crystalline structuremay be employed to grip and mechanically exfoliate layer(s) of graphiteto produce one or more layers of graphene. For example, ice may beemployed as a crystalline structure. Water ice is a well-researchedsubstance with mature regulations and risk data. The temperature andpressure at which ice forms is achievable with minimal energyexpenditure and minimal risk to personnel and the environment. Thelabor, materials and equipment required by this solution are inexpensiveand may be scaled readily to bulk industrial production for sale at acost-effective price point.

In the following description and in the figures, like elements areidentified with like reference numerals. The use of “e.g.,” “etc.,”,“or” and “the like” indicates non-exclusive alternatives withoutlimitation, unless otherwise noted. The use of “having”, “comprising”,“including” or “includes” means “including, but not limited to,” or“includes, but not limited to,” unless otherwise noted.

Multiple entities listed with “and/or” should be construed in the samemanner, i.e., “one or more” of the entities so conjoined. Other entitiesmay optionally be present other than the entities specificallyidentified by the “and/or” clause, whether related or unrelated to thoseentities specifically identified. Thus, as a non-limiting example, areference to “A and/or B,” when used in conjunction with open-endedlanguage such as “comprising” can refer, in one implementation, to Aonly (optionally including entities other than B); in anotherimplementation, to B only (optionally including entities other than A);in yet another implementation, to both A and B (optionally includingother entities). These entities may refer to elements, actions,structures, steps, operations, values, and the like.

Various aspects of the above referenced system are described in detailherein by way of examples, rather than by way of limitation.

FIG. 1 illustratively depicts a series of contacts 100 between agraphite grain 102 and a fluid medium 104 at a molecular scale. FIG. 1depicts four series of steps (steps A-D) for exfoliating a graphitegrain described in detail below. The series of contacts 100 includes acrystalline structure layer 106, a crystalline structure 108, and anexfoliated graphite grain 110. For the purpose of simplicity, FIG. 1depicts a two-dimensional side view with individual atoms depicted ascircles and bonds between atoms depicted as lines. For simplicity andbrevity, FIG. 1 depicts a graphite grain 102 including multi-layergraphene with five vertical layers of graphene stacked next to eachother and held together by van der Waals forces. As discussed above,each graphene layer includes carbon atoms arranged in a hexagonal bondpattern. It should be noted that the process described below is expectedto respond similarly regardless of the number of layers in the graphitegrain 102. Therefore, more or less layers than depicted may be used.Furthermore, although one graphite grain 102 is depicted in FIG. 1 forsimplicity and brevity, additional graphite grains may be interactingwith the fluid medium 104.

In step A, the graphite grain 102 is suspended as a solid particle in afluid medium 104. As depicted in FIG. 1 , the fluid medium 104 mayinclude a plurality of constituents (e.g., atoms, ions, or molecules).In one implementation, the fluid medium 104 may be a solution thatincludes water. In another implementation, the fluid medium 104 may bean aqueous solution containing water buffered by a buffering agent, suchas acetic acid, citric acid, formic acid, borate, or potassiumdihydrogen phosphate. In a third implementation, the fluid medium 104may include an abrasive material, such as silica, calcite, or diamonddust. The fluid medium 104 may include a surfactant (e.g., soap, analkyl sulfate, an alkylbenzene sulfonate, a lignosulfonate,n-methyl-2-pyrrolidone, sodium cholate, etc.) to alter thecharacteristics of the fluid medium 104. The fluid medium 104 may alsoinclude a freezing point depressant (e.g., ethylene glycol, methylalcohol, propyl alcohol or derivatives thereof, ethyl alcohol, sugar,etc.) to reduce the freezing temperature of the fluid medium 104. Inother implementations, the fluid medium 104 may be other fluids, otherfluid solutions or other solutions existing in other state(s).

After step A, in step B of FIG. 1 , a thermal sink such as a coolingplate (not depicted) is used to cool the fluid medium 104 at or below afreezing temperature. As used herein, “freezing temperature” refers tothe temperature at which a material may begin to change thermodynamicphase from a liquid to a solid. The process of changing thermodynamicphase from a liquid to a solid is also referred to as “solidifying.” Aliquid solidifying into a crystalline structure may preferentiallysolidify onto other solids in a process referred to as “nucleation.”Solids onto which a crystalline structure may begin to solidify arereferred to as “nucleation sites.” In the present disclosure, as thefluid medium 104 solidifies, two or more of the fluid medium 104molecules bond to one another in a repeating pattern to form acrystalline structure layer 106.

In an implementation, the freezing temperature is that of pure water,which is approximately 0° Celsius under one atmosphere of pressure. Inresponse to cooling at or below the freezing temperature, the fluidmedium 104 begins to solidify to a crystalline structure layer 106. Thefluid medium 104 may solidify to a crystalline structure layer 106 on anucleation site. The graphite grain 102 may serve as a nucleation sitefor the crystalline structure layer 106. In an implementation, the fluidmedium 104 may be selected such that the crystalline structure layer 106adheres to an outer layer of the graphite grain 102 as the fluid medium104 freezes.

After step B, in step C of FIG. 1 , the thermal sink (not depicted)continues to cool the fluid medium 104 below the freezing temperature toremove latent heat and cause additional freezing of the fluid medium104. In response to the continued cooling, the fluid medium 104continues to solidify, and the crystalline structure layer 106 grows toform a crystalline structure 108. In an implementation, the crystallinestructure 108 may continue to grow (e.g., get larger and the fluidmedium 104 molecules continue to bond with others) until the fluidmedium 104 is completely solidified or the thermal sink (not depicted)ceases to cool the fluid medium 104. The thermal sink (not depicted) maycease to cool the fluid medium 104 in response to a command from a user,in response to an automated command, or upon loss of power.

After step C, in step D, the device to create agitation (i.e., theagitator) (not depicted) continues to agitate the graphite grain 102,the crystalline structure 108, and the fluid medium 104. As used herein,“agitate” refers to raising the kinetic energy of a substance. Forexample, a rotating blade or vibration source may be used to agitate asubstance by introducing kinetic energy. In an implementation, continuedgrowth of the crystalline structure 108 may increase the force inducedby resistance to motion within a fluid (also referred to as “fluiddrag”) between the crystalline structure 108 and the fluid medium 104.As the fluid drag increases, a force is transferred from the crystallinestructure 108 to the graphite grain 102. Ultimately, the tensiontransferred to the graphite grain 102 may exceed the forces holding thelayers of graphite together (also referred to as “interlayer bondstrength”) created by the van der Waals forces. As a result, theinterlayer bond strength may be overcome and the crystalline structure108 may thus be mechanically separated from the graphite grain 102.

In an implementation, the fluid medium 104 is selected such that theadhesive strength of the crystalline structure 108 is greater than theinterlayer bond strength of the graphite grain 102. As a result, theouter layer of the graphite grain 102, to which the crystallinestructure 108 is adhered, may be exfoliated from the graphite grain 102with the crystalline structure 108. Following this exfoliation, anexfoliated graphite grain 110 is divided away from the graphite grain102.

In an implementation, the newly exposed outer layer of the exfoliatedgraphite grain 110 may then serve as a nucleation site upon which grainsbegin to solidify for continued development of a crystalline structurelayer 106 and a crystalline structure 108. Thus, steps A through D inFIG. 1 may be repeated upon the exfoliated graphite grain 110 to furtherexfoliate the graphite. Through repetition of steps A through D (i.e.,performing steps A through D and repeating these steps again and again),the series of contacts 100 as described above may reduce graphite tonanographite, multi-layer graphene, and ultimately graphene. In animplementation, graphite is exfoliated to multi-layer graphene withintwo hours of repetition of steps A through D. Graphite may be exfoliatedto graphene within any other time frame in other implementations.Additional details are provided below regarding several implementationswhereby the technique described above may be achieved in a scalable andcost-effective manner.

FIG. 2 illustratively depicts an apparatus 200 for exfoliating graphite.The apparatus 200 for exfoliating graphite includes a vessel 202, anagitator 216, and a thermal sink 218. The vessel 202 includes orotherwise houses a fluid medium 226 and at least a graphite grain 228.The agitator 216 includes a motor 212, an input shaft 210, a gear box208, and an output shaft 206. The thermal sink 218 includes a coolantinlet 220, a coolant outlet 222, and a chiller 224. The motor 212includes a support arm 204 and a motor electric input 214. The chiller224 includes a chiller electric input 230.

The vessel 202 may be created or otherwise manufactured to hold anyvolume of a fluid medium as determined by a designer of the apparatus200. In an implementation, the vessel 202 is constructed from one ormore, or a combination, of the following materials: metal, plastic orpolymer, or glass. The vessel 202 may be insulated using an insulationsuch as fiberglass, cotton, or Cryogel® which is aerogel cryogenicinsultation to reduce undesired heat transfer.

A graphite grain 228 and a fluid medium 226 may be transferred into thevessel 202 to form a mixture. The mixture may contain any ratio of thegraphite grain 228 and the fluid medium 226. The volume of the fluidmedium 226 may be any volume that is containable by the vessel 202 andthe vessel 202 may vary in size. The fluid medium 226 may be any fluid,non-fluid, or a combination thereof. The fluid medium 226 may at leastpartially solidify into a crystalline structure in response to coolingbelow a freezing temperature. In an implementation, the fluid medium 226is deionized water meeting a minimum purity standard of at least theAmerican Society for Testing and Materials (ASTM) Type IV as describedin ASTM D1193-91. In another implementation, the fluid medium 226 is asolution containing water and at least one solute such as chloride,fluoride, or one or more minerals. As used herein, “solute” refers to aminor component in a solution, dissolved in a solvent. In a thirdimplementation, the fluid medium 226 is another liquid. In yet otherimplementations, the fluid medium 226 may be a non-fluid or acombination of a fluid and non-fluid medium.

The graphite grain 228 may be added to the vessel 202 prior to, at thesame time as, or following the addition of the fluid medium 226. In animplementation, the graphite grain 228 may be cooled prior tointroduction into the vessel 202. In another implementation, thegraphite grain 228 may be equalized in temperature with an ambienttemperature such as 25° Celsius or another temperature. The graphitegrain 228 may be in a powdered form (e.g., a powdered solid form) havingan average flake size. In an implementation, the graphite grain 228 hasan average flake size of between 5 micrometers and 100 micrometers. Inanother implementation, the graphite grain 228 has an average flake sizeof more than 100 micrometers. In a third implementation, the graphitegrain 228 is a heterogenous plurality of graphite grains of any sizecontainable by the vessel 202.

The agitator 216 may be at least temporarily affixable, permanentlyaffixable or removably affixable to the vessel 202. In animplementation, the agitator 216 includes one or more rotors that are incontact with the fluid medium 226 to increase agitation and that are atleast occasionally in contact with the graphite grain 228. A rotor mayinclude one or more blades extending outward from a shaft, such that asthe shaft rotates the blades move through the fluid medium 226. Themovement of the one or more blades may increase the kinetic energy ofthe fluid medium 226 to cause agitation. Through rotation, the agitator216 may initiate agitation in the fluid medium 226 and occasionalcontact with the graphite grain 228 such that the graphite grain 228moves relative to the fluid medium 226.

As used herein, “circular rotation” refers to a periodic motion of oneor more objects along the circumference of a circle or rotation along acircular path. Circular rotation may be uniform (e.g., with constantangular rate of rotation and constant speed) or non-uniform with achanging rate of rotation or changing speed. In an implementation, acircular rotation is produced by the motion of a motor 212. The motor212 may be driven by or otherwise powered by a chemical fuel such asgasoline, liquefied petroleum gas (LPG) (i.e., propane), or diesel fuel.Alternatively, the motor 212 may be an electric motor driven by a motorelectric input 214 which may couple to a wired electrical source and/orto a battery. In an implementation, the motor 212 is an alternatingcurrent (“A/C”) motor. The motor 212 may be supported structurally by asupport arm 204. The support arm 204 may be constructed of any kind ofmaterial that can support the motor 212. The support arm 204 maybeconstructed of a metal, plastic, rubber, cardboard, or a combinationthereof.

An input shaft 210 may be at least temporarily coupled, permanentlycoupled or removably coupled at one end to the motor 212. The inputshaft 210 may be welded, joined via a temporary or permanent joint, orotherwise connected to the motor 212. The input shaft 210 may beconstructed of any kind of material that can laterally support the motor212. The input shaft 210 maybe constructed of a metal, plastic, rubbercardboard, or a combination thereof. In an implementation, an opposingend of the input shaft 210 is at least temporarily coupled, permanentlycoupled or removably coupled to a gear box 208. The input shaft 210 maybe welded, joined via a temporary or permanent joint, or otherwiseconnected to the gear box 208. The gear box 208 may include two or moregears (not depicted). Each gear (not depicted) in the gear box 208 mayhave a specific number of teeth. The rotation of a gear may beinterlocked with one or more other gears such that the rotation of a onegear transfers force through the teeth to produce rotation of one ormore other gears. The ratio of the number of teeth between one gear andanother gear is known as a “gear ratio.” The aggregated gear ratios ofall interlocked gears in the gear box 208 is referred to as the “gearratio” of the gear box 208. The gear box 208 operates to mechanicallyconvert the rotation of the input shaft 210 to a second rotation, suchthat the rate of the second rotation is different from the rate of therotation of the input shaft 210 according to a gear ratio. In animplementation, the gear box 208 may mechanically convert the rotationof the input shaft 210 to a second rotation, such that the direction ofthe second rotation is different from the direction of the rotation ofthe input shaft 210 according to an angle. The gear box 208 may be atleast temporarily coupled, permanently coupled or removably coupled toan output shaft 206. The output shaft 206 may be welded, joined via atemporary or permanent joint, or otherwise connected to the gear box208.

In an alternative implementation (not depicted), the motor 212 may be atleast temporarily coupled, permanently coupled or removably coupleddirectly to the output shaft 206 without having an input shaft. In suchan implementation, the rate of rotation of the motor 212 is the same orsubstantially the same (e.g., within +/−5%) as the rate of rotation ofthe output shaft 206 and the direction of rotation of the motor 212 isthe same or substantially the same (e.g., within +/−5%) as the directionof rotation of the output shaft 206.

In an implementation, the rate of rotation of the output shaft 206 maycontribute to the degree of agitation produced by the agitator 216. Inan implementation, one or more rotors are coupled to the output shaft206 to provide additional agitation. A rotor may include one or moreblades extending outward from a shaft, such that as the shaft rotatesthe blades move through the fluid medium 226. The movement of the one ormore blades may increase the kinetic energy of the fluid medium 226 tocause agitation. The degree of agitation produced by the agitator 216may be such that, as crystalline structures form in the fluid medium 226in response to cooling, the agitation produces shear forces applied tothe crystalline structure sufficient to overcome an internal bondstrength of the graphite grain 228 as depicted in FIG. 1 above.

In an implementation, the fluid medium 226 is configured such that, inresponse to being cooled below a freezing temperature of the fluidmedium 226, the fluid medium 226 at least partially solidifies to acrystalline structure and adheres to an outer layer of the graphitegrain 228. The thermal sink 218 is able to cool the fluid medium 226 andthe graphite grain 228 to below the freezing temperature of the fluidmedium 226.

A portion of the thermal sink 218 may be affixed to the bottom of thevessel 202. The vessel 202 may transfer heat into the thermal sink 218.Heat may be transferred into the thermal sink through any of conduction,convection, radiation, or a combination thereof. The portion of thethermal sink 218 that is affixed to the bottom of the vessel 202 maycontain passages (not shown) that permit flow of a liquid coolantthroughout the passages. In an implementation, the liquid coolant is oneof sodium chloride, ethylene glycol, isopropyl alcohol, methyl alcohol,butyl alcohol, ethyl alcohol, liquid nitrogen, or another liquid orcombination of liquids.

The thermal sink 218 may include a coolant inlet 220 and a coolantoutlet 222 that are at least temporarily coupled, permanently coupled orremovably coupled at one end to the portion of the thermal sink 218affixed to the bottom of the vessel 202. In an implementation, thecoolant inlet 220 and the coolant outlet 222 include pipes that permitflow of the liquid coolant. The pipes may be constructed of metal,plastic, rubber, cardboard, or a combination thereof. The coolant inlet220 and the coolant outlet 222 may be insulated using an insulation suchas fiberglass, cotton, or Cryogel® which is aerogel cryogenicinsultation to reduce heat transfer into or out of the coolant inlet 220or the coolant outlet 222.

The coolant inlet 220 and the coolant outlet 222 may be at leasttemporarily coupled, permanently coupled or removably coupled at anotherend to a chiller 224. The chiller 224 is constructed of metal, plastic,rubber, cardboard, or a combination thereof. In an implementation, thechiller 224 is able to cool the liquid coolant in the coolant outlet 222away from the apparatus 200 and return liquid coolant at a lowertemperature in the coolant inlet 220. The chiller 224 may be a tankcontaining a cryogenic fluid such as liquid nitrogen. In an alternativeimplementation, the chiller 224 is an electric apparatus for coolingfluids, having a chiller electric input 230. The chiller 224 may coolthe liquid coolant at a constant (same) rate. In an implementation, thechiller 224 may instead cool the liquid coolant at a variable rate.

By cooling the liquid coolant, the thermal sink 218 may cool the fluidmedium 226 and the graphite grain 228 to below a freezing temperature ofthe fluid medium 226. Thus, by a combination of cooling and agitation,the apparatus 200 brings about formation and exfoliation of crystallinestructures in the fluid medium 226 and exfoliation of the graphite grain228. However, discussed herein, other apparatuses may be employed toachieve a similar or same effect in a scalable and cost-efficientmanner.

FIG. 3 illustratively depicts an apparatus 300 for exfoliating graphite.Components in apparatus 300 may be similar to or the same as those ofapparatus 200 and therefore, the description of the components inapparatus 200 also apply to the components in apparatus 300. Theapparatus 300 for exfoliating graphite includes a vessel 302, anagitator 304, and a thermal sink 308. The vessel 302 includes a fluidmedium 312 and a graphite grain 310. The agitator 304 includes anagitator electric input 306.

The vessel 302 may be created or otherwise manufactured to hold anyvolume of a fluid medium 312 as determined by a designer of theapparatus 300. In an implementation, the vessel 302 is constructed fromone or more of metal, plastic or polymer, or glass. The vessel 302 maybe insulated to reduce undesired heat transfer.

A graphite grain 310 and a fluid medium 312 may be transferred into thevessel 302 to form a mixture. The volume of the fluid medium 312 may beany volume that is containable by the vessel 302 and the vessel 302 mayvary in size. The fluid medium 312 may be any fluid wherein the fluidmedium 312 at least partially solidifies into a crystalline structure(not shown) in response to cooling below a freezing temperature. In animplementation, the fluid medium 312 is deionized water meeting aminimum purity standard. In another implementation, the fluid medium 312is a solution containing water and at least one solute. As used herein,“solute” refers to a minor component in a solution, dissolved in asolvent. In a third implementation, the fluid medium 312 is anotherliquid.

The graphite grain 310 may be added to the vessel 302 prior to orfollowing the addition of the fluid medium 312. The graphite grain 310may be cooled prior to introduction into the vessel 302. The graphitegrain 310 may be in a powdered form having an average flake size. In animplementation, the graphite grain 310 has an average flake size ofbetween 5 micrometers and 100 micrometers. In another implementation,the graphite grain 310 has an average flake size of more than 100micrometers. In a third implementation, the graphite grain 310 is aheterogenous plurality of graphite grains of any size containable by thevessel 302.

The agitator 304 is at least temporarily affixed, removably affixed orpermanently affixed to the vessel 302. In an implementation, theagitator 304 includes one or more vibrators (305) in contact with anexternal surface of the vessel 302. Through vibration, the agitator 304may initiate agitation in the fluid medium 312 such that the graphitegrain 310 moves relative to the fluid medium 312.

The frequency and amplitude of vibration of the agitator 304 contributeto the degree of agitation produced by the agitator 304. In animplementation, the agitator 304 is able to produce a frequency ofvibration greater than 40 kHz. The degree of agitation produced by theagitator 304 may be configured such that, as crystalline structures formin the fluid medium 312 in response to cooling, the agitation issufficient to overcome an internal bond strength of the graphite grain310 as depicted in FIG. 1 above.

In an implementation, the fluid medium 312 is configured such that, inresponse to being cooled below a freezing temperature, the fluid medium312 at least partially solidifies to a crystalline structure and adheresto an outer layer of the graphite grain 310. As used herein, “freezingtemperature” refers to the temperature at which a material may begin tochange thermodynamic phase from a liquid to a solid. The process ofchanging thermodynamic phase from a liquid to a solid is also referredto as “solidifying.” A liquid solidifying into a crystalline structuremay preferentially solidify onto other solids in a process referred toas “nucleation.” Solids onto which a crystalline structure may begin tosolidify are referred to as “nucleation sites.” In the presentdisclosure, as the fluid medium 312 solidifies, two or more of the fluidmedium 312 molecules bond to one another in a repeating pattern to forma crystalline structure layer (not depicted). The thermal sink 308 isable to cool the fluid medium 312 and the graphite grain 310 to below afreezing temperature. In an implementation, the freezing temperature isthat of pure water, which is approximately 0° Celsius under oneatmosphere of pressure.

The thermal sink 308 may be a substance having an instant temperaturesufficiently low to cool the fluid medium 312 to below a freezingtemperature. In an implementation, the thermal sink 308 is added to thefluid medium 312 after the fluid medium 312 and the graphite grain 310have been introduced into the vessel 302. The thermal sink 308 may be asolid substance or a liquid substance. In an implementation, the thermalsink 308 is a volume of solidified carbon dioxide, also known as dryice. In another implementation, the thermal sink 308 is a volume of acryogenic liquid such as liquid nitrogen, liquid oxygen, or liquidhelium.

By simple heat transfer, the thermal sink 308 may cool the fluid medium312 and the graphite grain 310 to below a freezing temperature. Thus, bya combination of cooling and agitation, the apparatus 300 brings aboutformation and cleaving of crystalline structures in the fluid medium 312and exfoliation of the graphite grain 310. However, as will be discussedbelow, still other apparatuses may be employed to achieve the sameeffect in a scalable and cost-efficient manner.

FIG. 4 illustratively depicts an apparatus 400 for exfoliating graphite.Components in apparatus 400 may be similar to or the same as those ofapparatus 200 and apparatus 300 and therefore, the description of thecomponents in apparatus 200 and apparatus 300 also apply to thecomponents in apparatus 400. The apparatus 400 for exfoliating graphiteincludes a vessel 422, an agitator 402, a thermal sink 406, and agraphite block 408. The vessel 422 includes a fluid medium 418 and agraphite grain 420. The agitator 402 includes an agitator electric input404. The thermal sink 406 includes a coolant inlet 410, a coolant outlet412, and a chiller 414. The chiller 414 includes a chiller electricinput 416.

The vessel 422 forms the core of the apparatus 400. The vessel 422 maybe created or otherwise manufactured to hold any volume of a fluidmedium 418 as determined by a designer of the apparatus 400. In animplementation, the vessel 422 is constructed from one or more of metal,plastic or polymer, or glass. The vessel 422 may be insulated using aninsulation such as fiberglass, cotton, or Cryogel® which is aerogelcryogenic insultation to reduce heat transfer out of the vessel 422.

A graphite grain 420 and a fluid medium 418 may be transferred into thevessel 422 to form a mixture. The volume of the fluid medium 418 may beany volume containable by the vessel 422. The fluid medium 418 may beany fluid wherein the fluid medium 418 at least partially solidifiesinto a crystalline structure (not shown) in response to cooling below afreezing temperature. In an implementation, the fluid medium 418 isdeionized water meeting a minimum purity standard. In anotherimplementation, the fluid medium 418 is a solution containing water andat least one solute. As used herein, “solute” refers to a minorcomponent in a solution, dissolved in a solvent. In a thirdimplementation, the fluid medium 418 is another liquid.

The graphite grain 420 may be added to the vessel 422 prior to orfollowing the addition of the fluid medium 418. The graphite grain 420may be cooled prior to introduction into the vessel 422. The graphitegrain 420 may be in a powdered form having an average flake size. In animplementation, the graphite grain 420 has an average flake size ofbetween 5 micrometers and 100 micrometers. In another implementation,the graphite grain 420 has an average flake size of more than 100micrometers. In a third implementation, the graphite grain 420 is aheterogenous plurality of graphite grains of any size containable by thevessel 422.

The agitator 402 is at least temporarily affixed, removably affixed orpermanently affixed to the thermal sink 406. In an implementation, theagitator 402 includes one or more vibrational units in contact with thetop of the thermal sink 406. Through vibration, the agitator 402 mayinitiate agitation in the fluid medium 418 such that the graphite grain420 moves relative to the fluid medium 418.

The frequency and amplitude of vibration of the agitator 402 contributeto the degree of agitation produced by the agitator 402. In animplementation, the agitator 402 is able to produce a frequency ofvibration greater than 40 kHz. The degree of agitation produced by theagitator 402 may be such that, as crystalline structures form in thefluid medium 418 in response to cooling, the agitation is sufficient toovercome an internal bond strength of the graphite grain 420.

In an implementation, the fluid medium 418, in response to being cooledbelow a freezing temperature, the fluid medium 418 at least partiallysolidifies to a crystalline structure such as an ice grain and mayadhere to an outer layer of the graphite grain 420. The thermal sink 406is able to cool the fluid medium 418 and the graphite grain 420 to belowthe freezing temperature.

A portion of the thermal sink 406 may be affixed to the bottom of theagitator 402. The agitator 402 may conduct heat into the thermal sink406. The portion of the thermal sink 406 affixed to the bottom of theagitator 402 may contain passages (not shown) to permit flow of a liquidcoolant. In an implementation, the liquid coolant is one of ethyleneglycol, isopropyl alcohol, methyl alcohol, butyl alcohol, liquidnitrogen, or another liquid.

The thermal sink 406 may include a coolant inlet 410 and a coolantoutlet 412 at least temporarily coupled, removably coupled orpermanently coupled at one end to the portion of the thermal sink 406affixed to the bottom of the agitator 402. In an implementation, thecoolant inlet 410 and the coolant outlet 412 are pipes that permit flowof the liquid coolant. The coolant inlet 410 and the coolant outlet 412may be insulated to reduce undesired heat transfer.

The coolant inlet 410 and the coolant outlet 412 may be at leasttemporarily coupled, removably coupled or permanently coupled at anotherend to a chiller 414. In an implementation, the chiller 414 is able tocool the liquid coolant in the coolant outlet 412 away from theapparatus 400 and return liquid coolant at a lower temperature in thecoolant inlet 410. In an implementation, the chiller 414 may be able toreturn liquid coolant in the coolant inlet 410 at a temperature below−20° Celsius. The chiller 414 may be a tank containing a cryogenicmaterial such as liquid nitrogen, liquid hydrogen, liquid oxygen, orliquid helium. Alternatively, the chiller 414 may be a hopper containingsolidified carbon dioxide, also known as dry ice. In otherimplementations, the chiller 414 may be any other mechanism that cancool the liquid coolant. In an implementation, the chiller 414 is anelectric apparatus for cooling fluids, having a chiller electric input416. The chiller 414 may cool the liquid coolant at a constant rate. Inan implementation, the chiller 414 may instead cool the liquid coolantat a variable rate.

In an implementation, the coolant outlet 412 may be directed to a vent(not shown). In this implementation, the chiller 414 supplies a chilledgas to the coolant inlet 410. The chilled gas may be passed through thefluid medium 418 as a plurality of bubbles to cool the fluid medium 418through conduction. In an implementation, the plurality of bubbles mayact as nucleation sites, as described above, for the formation ofcrystalline structures. The chilled gas may include at least one of air,helium, nitrogen, neon, argon, or carbon dioxide. The coolant outlet 412may also be at least partially directed to a gas recapture system (notshown).

A graphite block 408 may be at least temporarily affixed, removablyaffixed or permanently affixed to the bottom of the thermal sink 406. Inan implementation, the graphite block 408 is held at least partially influid contact with the surface of the fluid medium 418. As graphite is athermal conductor, the graphite block 408 may serve to transfer heatfrom the fluid medium 418 into the thermal sink 406. As the fluid medium418 cools to below a freezing temperature, crystalline structures suchas ice grains may form on the surface of the graphite block 408. Theagitation produced by the agitator 402 may be sufficient to overcome aninterlayer bond strength in the graphite block 408 such that thecrystalline structures are mechanically separated from the graphiteblock 408. Thus, the graphite block 408 may be at least a partial sourceof the graphite grain 420.

By cooling the liquid coolant, the thermal sink 406 may cool thegraphite block 408, the fluid medium 418, and the graphite grain 420 tobelow a freezing temperature. Thus, by a combination of cooling andagitation, the apparatus 400 brings about formation and cleaving ofcrystalline structures in the fluid medium 418 and exfoliation of thegraphite grain 420. Thus, as has been discussed above, severalapproaches may be employed to achieve the same effect in a scalable andcost-efficient manner.

Steps used to exfoliate graphite are described herein below with respectto FIG. 5 .

FIG. 5 is a flow diagram illustrating a method 500 for exfoliatinggraphite. In one implementation, the method 500 may be performed usingany of the apparatuses for exfoliating graphite described in thisapplication. For example, apparatus 200, apparatus 300, and/or apparatus400 depicted in FIGS. 2, 3, and 4 , respectively, can perform the stepsof method 500. Furthermore, the method 500 may also be performed byanother apparatus(es) for exfoliating graphite.

For simplicity of explanation, the methods of this disclosure aredepicted and described as a series of acts. However, acts in accordancewith this disclosure can occur in various orders and/or concurrently,and with other acts not presented and described herein. Furthermore, notall illustrated acts may be required to implement the methods inaccordance with the disclosed subject matter. In addition, those skilledin the art will understand and appreciate that the methods couldalternatively be represented as a series of interrelated states via astate diagram or events.

Referring to FIG. 5 , method 500 begins at block 502 where a graphitegrain and a fluid medium are transferred into a vessel. For example, agraphite grain (228, 310, and/or 420) and a fluid medium (226, 312,and/or 418) are transferred into a vessel (202, 302, and/or 422). Thevessel (202, 302, and/or 422) may receive and store any quantity of thegraphite grain (228, 310, and/or 420) and fluid medium (226, 312, and/or418) according to a ratio. The graphite grain (228, 310, and/or 420) andthe fluid medium (226, 312, and/or 418) may be introduced into thevessel (202, 302, and/or 422) by a transfer system or by manual deliveryor another process.

At block 504, the graphite grain and the fluid medium are agitated bythe agitator such that the graphite grain moves relative to the fluidmedium. For example, the agitator (216, 304, and/or 402) agitates thegraphite grain (228, 310, and/or 420) and the fluid medium (226, 312,and/or 418) such that the graphite grain (228, 310, and/or 420) movesrelative to the fluid medium (226, 312, and/or 418). The agitator (216,304, and/or 402) may cause the graphite grain (228, 310, and/or 420) tomove relative to the fluid medium (226, 312, and/or 418) at a stirringrate. In an implementation, the stirring rate is constant (e.g., within+/−5%) throughout a cycle of operation. In another implementation, twoor more stirring rates or directions may be employed during a cycle ofoperation.

At block 506, a chiller chills the graphite grain and the fluid mediumsuch that the fluid medium at least partially solidifies into an icegrain. For example, the thermal sink (218, 308, and/or 406) cools thegraphite grain (228, 310, and/or 420) and the fluid medium (226, 312,and/or 418) to temperature below a freezing temperature. In animplementation, the fluid medium (226, 312, and/or 418) is configuredsuch that the fluid medium (226, 312, and/or 418) at least partiallysolidifies to a crystalline structure (108) such as an ice grain inresponse to cooling below the freezing temperature of the fluid medium(226, 312, and/or 418). In a further implementation, the fluid medium isable to adhere to an outer layer of the graphite grain as the fluidmedium (226, 312, and/or 418) solidifies to a crystalline structure(108) such as an ice grain. In an implementation, the crystallinestructure (108) is transferred into the vessel (202, 302, and/or 422)from an external source.

At block 508, the agitator agitates the graphite grain, the ice grain,and the fluid medium to induce a contact between the graphite grain andthe ice grain to exfoliate the graphite grain. For example, the agitator(216, 304, and/or 402) agitates the graphite grain (228, 310, and/or420), the crystalline structure (108), and the fluid medium (226, 312,and/or 418) together to induce a contact between the graphite grain(228, 310, and/or 420) and the crystalline structure (108) to exfoliatethe graphite grain. In an implementation, the thermal sink (218, 308,and/or 406) continues to cool the graphite grain (228, 310, and/or 420)and the fluid medium (226, 312, and/or 418) during block 508 such thatthe crystalline structure (108) continues to grow in size, such as from5 micrometers to 10 micrometers in diameter. In response to increasedfluid drag during agitation, a force is transferred to the graphitegrain (228, 310, and/or 420) and the interlayer bond strength of thegraphite grain caused by van der Waals forces is overcome.

When the interlayer bond strength of the graphite grain (228, 310,and/or 420) is overcome, the crystalline structure (108) may bemechanically separated from the graphite grain (228, 310, and/or 420) bya mechanical force. Mechanical forces on the crystalline structure (108)and the graphite grain (228, 310, and/or 420) may include any of fluidfriction, a kinetic contact with an agitator, a kinetic contact withanother crystalline structure (108), or kinetic contact with anothergraphite grain (228, 310, and/or 420). In an implementation, the fluidmedium (226, 312, and/or 418) is configured such that the adhesivestrength of the crystalline structure is greater than the interlayerbond strength of the graphite caused by van der Waals forces. As aresult, the mechanical separation of the crystalline structure from thegraphite grain (228, 310, and/or 420) is expected to cleave the graphitegrain (228, 310, and/or 420), with at least one of the outer layers ofthe graphite grain (228, 310, and/or 420) remaining adhered to thecrystalline structure. Thus, at least one outer layer of the graphitegrain (228, 310, and/or 420) may be exfoliated with the crystallinestructure.

In an implementation, the steps described in block 504 to block 508 arerepeated recurringly during at least a portion of the operating cycle ofthe apparatus for exfoliating graphite. Thus, the outer layers of thegraphite grain (228, 310, and/or 420) exposed by exfoliation may receivefurther crystalline structure adhesion and exfoliation. In animplementation, the graphite grain (228, 310, and/or 420) may be reducedto nanographite, multi-layer graphene, and finally to graphene. In animplementation, the graphite grain (228, 310, and/or 420) is reduced tomulti-layer graphene within two hours.

In yet another implementation, to exfoliate a graphite grain, thefollowing steps are taken. A mixture is transferred into a vessel. Themixture includes a graphite grain and an ice grain. The vessel includesan agitator. The mixture is agitated by the agitator to induce a contactbetween the graphite grain and the ice grain to exfoliate the graphitegrain.

In yet another implementation, to exfoliate a graphite grain, thefollowing steps are taken. A mixture is transferred into a vessel. Themixture includes a graphite grain and a fluid medium. The vesselincludes an agitator and a chiller. The mixture is chilled by thechiller such that the fluid medium at least partially solidifies into anice grain. The mixture is agitated by the agitator to induce a contactbetween the graphite grain and the ice grain to exfoliate the graphitegrain.

In an implementation, the agitator includes a rotor. In animplementation, the rotor includes a first blade and a second blade.

In an implementation, the agitator includes a vibrator.

In an implementation, the fluid medium includes a first fluid where thefirst fluid includes water. The fluid medium further includes a secondfluid. The second fluid includes at least one of ethylene glycol,n-methyl-2-pyrrolidone, isopropyl alcohol, methyl alcohol, butylalcohol, or ethyl alcohol. In another implementation, the second fluidincludes at least one of air, nitrogen, argon, oxygen, or carbondioxide.

In an implementation, the fluid medium further includes a surfactant.The surfactant includes at least one of a soap, an alkyl sulfate, analkylbenzene sulfonate, a lignosulfonate, or sodium cholate.

While the implementations are susceptible to various modifications andalternative forms, specific examples thereof have been shown in thedrawings and are herein described in detail. It should be understood,however, that these implementations are not to be limited to theparticular form disclosed, but to the contrary, these implementationsare to cover all modifications, equivalents, and alternatives fallingwithin the spirit of the disclosure. Furthermore, any features,functions, steps, or elements of the implementations may be recited inor added to the claims, as well as negative limitations that define theinventive scope of the claims by features, functions, steps, or elementsthat are not within that scope.

What is claimed is:
 1. A method to exfoliate a graphite grain, themethod comprising: transferring a mixture into a vessel, wherein themixture comprises a graphite grain and an ice grain, and wherein thevessel comprises an agitator; and agitating the mixture by the agitatorto induce a contact between the graphite grain and the ice grain toexfoliate the graphite grain.
 2. The method of claim 1, wherein theagitator comprises a rotor.
 3. The method of claim 2, wherein the rotorcomprises a first blade.
 4. The method of claim 3, wherein the rotorfurther comprises a second blade.
 5. The method of claim 1, wherein theagitator comprises a vibrator.